(1) Field of the Invention
The present invention relates to a method for etching a polyamide shaped article as the preliminary treatment for plating the polyamide shaped article.
(2) Description of the Prior Art
Plated plastic articles have heretofore been used mainly as substitutes for metal articles in the field of ornamentation or decoration. Recently, however, also in the fields where good mechanical properties, heat resistance and weatherability are required, it has been desired to use plated plastic articles instead of metal articles. As such articles, there can be mentioned, for example, number plate holders, mirror holders and door handles of automobiles and printing types of high speed printers.
ABS resins are mainly used as the base material of these plated plastic articles, but because of inherent characteristics of ABS resins used as the base material, the application range is inevitably limited when plated plastic articles are used in the fields where the above-mentioned functional properties are required.
As means for eliminating this disadvantage, there have been proposed some methods in which a polyamide having properties excellent over those of an ABS resin is used as a base material and a polyamide shaped article is etched and then plated. According to these proposals, etching of polyamide shaped articles is performed by (1) a method in which a polyamide shaped article is dipped in chromic acid-sulfuric acid, (2) a method in which a polyamide shaped article is dipped in formic acid, (3) a method in which a polyamide shaped article is dipped in an iodide-potassium iodide solution or (4) a method in which a polyamide shaped article is dipped in sulfuric acid or hydrochloric acid.
According to any of these etching treatment methods, however, concavities suitable for plating are not formed on the surface of a polyamide shaped article, and therefore, the resulting plated article is defective in that the adhesion between the polyamide shaped article and the plated metal coating is poor (the T-peel strength as the criterion of the adhesion, described hereinafter, is lower than the practically necessary level of 0.8 Kg/cm) and the deviation of the adhesion is large.